On the relationships between applied force, photography technique, and the quantification of bruise appearance

Bruising is an injury commonly observed within suspect cases of assault or abuse, yet how a blunt impact initiates bruising and influences its severity is not fully understood. Furthermore, the standard method of documenting a bruise with colour photography is known to have limitations which influence the already subjective analysis of a bruise. This research investigated bruising using a standardised blunt impact, delivered to 18 volunteers. The resulting bruise was imaged using colour, cross polarised (CP) and infrared photography. Timelines of the L*a*b* colour space were determined from both colour and CP images for up to 3 weeks. Overall, no single photographic technique out-performed the others, however CP did provide greater contrast than colour photography. L*a*b* colour space timelines were not attributable any physiological characteristics. Whilst impact force negatively correlated with BMI (R² = 0.321), neither were associated with any measure of bruise appearance. Due to the inter-subject variability in the bruise response to a controlled infliction, none of the methods in the current study could be used to reliably predict the age of a bruise or the severity of force used in creating a bruise. A more comprehensive approach combining impact characteristics, tissue mechanics, enhanced localised physiological measures and improvements in quantifying bruise appearance is likely to be essential in removing subjectivity from their interpretation.